In metal ore resources inclusive of iron ore, a proportion of massive ore tends to decrease, and a proportion of powdery or tends to increase. At present, concentration such as flotation or magnetic separation is positively developed, so as to improve a grade of a low-grade ore in particular. Accordingly, such a tendency as mentioned above is anticipated to be marked more and more later.
There has been recently developed a so-called melt reduction process for producing a molten metal directly from a powdery ore. The melt reduction process comprises the steps of preliminarily reducing the powdery ore in a fluidized bed preliminary reducing furnace, then introducing the preliminarily reduced powdery ore obtained above into a melt reducing furnace filled with a carbonaceous solid reducing agent, and reducing and liquefying the preliminarily reduced powdery ore in the melt reducing furnace to produce the molten metal.
In the case that an inner diameter of the fluidized bed preliminary reducing furnace is large, a gas flow in a fluidized bed becomes nonuniform to cause a difficulty of proper fluidization. Therefore, in order to obtain a uniform gas flow, a gas dispersing plate having many gas dispersing holes is provided at a lower portion of the furnace where an inlet of a reducing gas is formed.
In the case of utilizing a high-temperature gas generated in the melt reducing furnace as the reducing gas for fluidization, there is a problem that the gas dispersing holes of the gas dispersing plate are closed by a large amount of dust contained in the high-temperature gas generated from the melt reducing furnace.
A solution of this problem is disclosed in Japanese Utility Model Laid-open Publication No. 62-29094, for example. FIG. 4 shows a fluidized bed gas dispersing device disclosed in this prior art. Referring to FIG. 4, reference numeral 3 generally designates this fluidized bed gas dispersing device provided in a preliminary reducing furnace 1. The dispersing device 3 is constructed of a plurality of bars 2 movable in a longitudinal direction thereof, which bars 2 are arranged in upper and lower horizontal planes so as to intersect with each other as viewed in plan. In removing a deposited substance 12 such as dust deposited on a surface of each bar 2, the bar 2 is sometimes drawn off, and the deposited substance 2 is then squeezed off.
However this prior art device has a defect that the bars are deformed by heat to result in impossibility of drawing of the bars.
Further, the present applicant has proposed in Japanese Patent Laid-open Publication No. 59-107185 a technique such that deformed bars arranged in rows are rotated to change an opening size between the adjacent ores of the deformed bars.
Thus, this technique is intended to change the opening size between the adjacent deformed bars. However, it is not intended to prevent the opening between the bars from being closed by the dust.